1977 Marshall JMP 2x12 50 watt combo model 2104, HUM!!! Easy fix.

This is a regular on my bench. The owner likes to run it good and hot so it cooked another 6550.

That part was easy. But the amp had an excessive amount of hum coming off the preamp. It was re-capped using JJ filters, but I tried replacing the one in the preamp to see if that solved it. Nope.

Here's the weird thing, the hum would change behavior. At one point it seemed like a ground loop hum. You could turn the master up and it was awful with the preamp all the way down. The preamp in the middle and it was tolerable. All the way up, unusable.

I tried replacing the preamp tubes to no avail. The client also told me the tone would get brittle then nice then back to harsh again. That was enough to remind me. It's simply the ground connections.

Marshall uses mechanical ground connections. In other words each ground point is soldered to a terminal that is connected to ground through nuts and bolts or the pots on the face of the amp. These can go bad over time. I re-soldered every ground point and it got better but I knew it could go even better than that. Then I heard this spark sound. I'm on the right path. Some ground point on the face of the amp was loose.

It's not unusual to need to pull all the pots and jacks, take a little sandpaper and sand lightly on the front of the amp, (make sure you get any metal dust out of there!) then re-connect everything good and tight. That can be a dramatic improvement.

Or.... Solder the ground rail directly to the chassis:

If you have a nice Weller iron like mine, set it as high as it will go (800 degrees). I used a scratch awl to make a rough surface where I soldered my new wire. Use rosin and heat that surface then hit it with solder. Test that solder to make sure it's not going to come off. Then solder your wire. Test that to make sure it's tight.

Amp is really quiet now. I've been letting it run all day. Tone is good, not slipping in and out of bad sound land. I'm happy.

And, I wrote this post largely to remind myself to check the grounds first. I tend to forget the simple fixes!

And yes, still one of the greatest rock n roll amps out there. These aren't terribly expensive either. Go get yourself one. You need to really know how to play to get the best out of it. These are simple devices unlike stuff with all that channel switching. What you do get is maximum tone. You get what you put into it. Play softer for clean tones, dig in for your nasty sounds!

-Jef

50's Russian 6SL7 and new 6SJ7 tubes, review. Nice glass!

Just a brief bit of impressions on some Russian glass I received recently from a great seller in Ukraine.

First up is the metal base Melz made 6SL7.

And the test LPs were Charlie Byrd Trio: Charlie's Choice and Stan Getz's Jazz Samba.

I usually have a set of run of the mill inexpensive nothing special RCA 6SL7 tubes burning away. I know how they sound as I spend hours listening to my setup. I'm also familiar with these records. They spend a good amount of time on my turntable.

My RCA tubes:

So how did they stack up against the RCA? The difference was pretty drastic. First let me say I wasn't expecting them to outshine what I have. I choose my hi-fi tubes carefully. If I don't like something it goes in my box to sell to guitar players.

The Melz has impressively low microphonics. Great for my phono stage. Sonically they are far more aggressive than my RCA. Very forward. Stan Getz's sometimes harsh tenor sound gets harsher, not in a bad way, just more in your face. I find the RCA tubes to be more clear and relaxed. Since I don't listen to much metal these days, the Melz tubes will go back in the box. I like to relax in my tiny universe.

I bet these will kick some ass in a guitar amp. I do have one Magnatone that used the 6SL7 tube. I have a new RCA in right now and prior to that I had a Sovtek there which I didn't find sounded objectionable at all. I have a feeling the Melz will melt some faces. I didn't find it objectionable for my hi fi either, I just prefer the RCA.

A word about 6SL7 tubes. The big octal 6SL7, 6SN7 tubes are my favorite for hi fi. They relax more for me than the more common and sought after 12AX7, 12AU7 which are obviously more in demand and more valuable. I built my own preamp to use 6SL7 tubes in the phono and line stage, 6SN7 for the cathode follower driving the power amp. I do not covet any vintage or modern preamps. I built mine 20 years ago from a Swedish schematic called "Remus". It's a fantastic circuit! Simple and honest. No Marantz 7 for me, this sounds better to my ears!

Ok next. A tube I'm really picky about. The 6SJ7. My 45 power amp uses these as a driver stage. Also my favorite guitar amps use these, Magnatone Varsity and "B" amplifier of my own design. They have something psychedelic about them, a shimmer, when in a guitar circuit. I thought it was an Echoplex I used to have but that's gone and that characteristic is still there on my recordings. I don't get it with other amps that don't use these.

So I have the fancy 5693 red RCA 6SJ7 tubes in mine. I love these for hi fi, guitar I prefer the standard 6SJ7. I have a set of metal base Sylvania 6SJ7s that I rejected in this circuit after 10 minutes. I missed the warmth and euphonic quality of these red tubes:

So I got these Russian babies. Cheap as a bag of fancy chips. No joke. A couple bucks each. How do they stack up?

I wasn't hopeful. But....they are pretty damned good! Again more forward and aggressive but not like the 6SL7 tubes. The sound was nice and round, not cold or harsh like my Sylvania tubes. In a pinch I would gladly burn these up. There is no markings on these, just a #7 in a box on the side. Charlie Byrd's guitar sounded nice and round, the percussion deep and warm with a nice top end. No, they don't beat my RCAs, but they don't offend me one bit either.

So, hope this was helpful! I will try these out in my guitar amps and do a bit about that as well. And remember just because something doesn't work for me doesn't mean it won't work for you. Give these a try if you are curious! I'd love to hear your impressions.

JB

StayTrem Jazzmaster/Jaguar bridge. Nice!

Just installed one of these today:

British made StayTrem Jazzmaster bridge. This was installed on a Made in Mexico "60's Jazzmaster" by Fender. The correct radius is 7.25". Make sure you don't get the 9.5" one for your Mexican, Japanese or American reissue guitar or your vintage one. It won't work!

My impressions? This is a great product! Super easy to install and the radius is spot on. I may buy one for my '58 myself. I've never had such an easy time setting up a Jazzmaster.

The slots are nice and deep, you can strum nice and hard without the strings popping out. The tone got stronger instantly too.

The big improvement is the string spacing. This is why I'd consider one myself. Mine has custom made brass Mustang style saddles:

Now look at these 2 photos and you'll see quite easily the strings on the StayTrem don't fly over the edge of your fretboard. First mine:

Next, theirs:

Now, I'm so used to mine that it doesn't bug me a bit. But if it bugs you, this bridge is a great solution to a few problems. Better stability, better tone, better sustain and better playability.

Do consider one! I'm a certified Jazzmaster fanatic and it gets a big thumbs up!


One more improvement......

Jazzmasters can gobble strings. Particularly the skinny E and B. I solder the ends on them cause they tend to unravel. Easy and quick trick I learned from Stevie Ray Vaughn's tech in an article about him. I haven't broken a string on mine in a long time and I'm a brute!

JB

The Stratocaster "Base" or "Bass" plate

This simple mod isn't for everyone. But I like it. The bridge pickup on a Stratocaster can simply vanish into thin air. I believe it was Lindy Fralin who started making these steel plates to fit under your bridge pickup. The Telecaster has one and my favorite guitar, the Fender Esquire, I don't miss having a neck pickup cause that bridge pickup is so full.

Installation is easy...

I scraped some wax from a candle I have onto the back of my pickup:

Step 2, sit plate on top of wax and melt with a soldering iron:

It's important to get the plate as flush as you can on the back of your pickup. Heat it up and press it with 2 objects like chopsticks or screwdrivers until the wax cools. If there is too much of a gap you can run into feedback issues. I've experienced this before....

Step 3: solder wire to the - or black wire and cut off excess:

Step 4. Put your guitar back together and rock out!

It's a fuller sound. Bass is a bit tighter but what I do notice is there is a Telecaster / Lap steel quality to the tone. More roundness to it. Try one! They only cost about ten bucks. If you don't dig it, carefully unsolder, re-heat and remove.

Buy one here: http://www.angela.com/lindyfralinbaseplateforstrat.aspx


Happy soldering! JB

Update, 10/5/17. I've been playing with this for just under a week and here are my impressions:

I'm not sure that it adds bass. But what I do hear is a rounder tone. It's definitely a bit more complex and stronger. Though, the contrast between the bridge pickup and others is reduced a bit. I can totally get behind the player who doesn't desire this as well. It's a bit like when you run a sound through an EQ and you turn the low mid dial back and forth. It has more body to it. I'll keep it in a while, take it out and see what I think then.